const {resolve} = require('path')
const HtmlWebpackPlugin = require('html-webpack-plugin')
const MiniCssExtractPlugin = require('mini-css-extract-plugin')
const OptimizeCssAssetsWebpackPlugin = require('optimize-css-assets-webpack-plugin')

// 定义nodejs环境变量：决定使用browserslist的哪个环境
process.env.NODE_ENV = 'development'

// 复用loader
const commonCssLoader = [
    MiniCssExtractPlugin.loader,
    'css-loader',
    {
        // 还需要在pack.json中定义browserslist
        loader: 'postcss-loader',
        options: {
            ident: 'postcss',
            plugins: () => [
                require('postcss-preset-env')()
            ]
        }
    }
]

module.exports = {
    entry: './src/js/index.js',

    output: {
        filename: 'js/built.js',
        path: resolve(__dirname, 'build')
    },

    module: {
        rules: [
            {
                test: /\.css$/,
                use: [
                    /*'style-loader',*/
                    ...commonCssLoader
                ]
            },

            {
                test: /\.less$/,
                use: [
                    /*'style-loader',*/
                    ...commonCssLoader,
                    'less-loader'
                ]
            },

            /*
                正常来讲，一个文件只能被一个loader处理。
                当一个文件要被多个loader处理，那么一定要指定loader的执行先后顺序：
                    先执行eslint   再执行babel

             */

            {
                // 在package.json中eslintConfig --> airbnb
                test: /\.js$/,
                exclude: /node_modules/,
                // 优先执行
                enfore: 'pre',
                loader: 'eslint-loader',
                options: {
                    fix: true
                }
            },

            {
                test: /\.js$/,
                exclude: /node_modules/,
                loader: 'babel-loader',
                options: {
                    presets: [
                        [
                            '@babel/preset-env',
                            {
                                useBuiltIns: 'usage',
                                corejs: {
                                    version: 3
                                },
                                targets: {
                                    chrome: '60',
                                    firefox: '60'
                                }
                            }
                        ]
                    ]
                }
            },

            {
                test: /\.(jpg|png|gif)/,
                loader: 'url-loader',
                options: {
                    limit: 8 * 1024,
                    name: '[hash:10].[ext]',
                    outputPath: 'imgs',
                    esModule: false
                }
            },

            {
                test: /\.html$/,
                loader: 'html-loader',
                options: {
                    esModule: false
                }
            },

            {
                exclude: /\.(js|less|css|html|jpg|png|gif)$/,
                loader: 'file-loader',
                outputPath: 'media'
            }
        ]
    },

    plugins: [
        new MiniCssExtractPlugin({
            filename: 'css/built.css'
        }),

        new OptimizeCssAssetsWebpackPlugin(),

        new HtmlWebpackPlugin({
            template: './src/index.js',
            minify: {
                collapseWhitespace: true,
                removeComments: true
            }
        }),


    ],

    mode: 'production'
}